Cutworms Turn Up in Southern Alberta — Which Fields to Check First

Adult army cutworm collected near Brooks June 8, 2012. Shelley Barkley

The first few days of May brought a surprise! The Twitterverse lit up with reports of cutworms in southern Alberta. The first report came in on a new alfalfa stand. In alfalfa we normally expect that the cutworms will be redbacked but in this case they were army cutworm. The second field was a winter triticale field that was destined for silage. The third field was winter wheat. In all cases the common factor was significant plant growth in the field in the previous fall right until freeze up.

Let’s go back in time for a moment to June of 2012. Some of you may remember a large influx of moths flying around in early June. They were flying everywhere, hiding under anything and everything, getting into houses and garages. Those were the adult army cutworm (Euxoa auxiliaris) and they were on their way to the foothills/mountains for the summer. The moths hang out there under rocks until fall. An interesting side note: these moths in their summer aestivation (like hibernation only in the summer) are important food source for grizzly bears. http://www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_9/French_French_Vol_9.pdf

Adult army cutworm collected near Brooks June 8, 2012. Shelley Barkley

In the fall the moths come back out onto the plains and lay their eggs in fields that have significant fall growth of crops and/or weeds. The eggs hatch and the larvae feed and grow in the fall. They overwinter in the larval (worm) stage. When the weather starts to warm up the cutworms become active very early and can cause significant damage in the spring.

All fall seeded crops should be scouted carefully to ensure the cutworm risk is assessed. Look for areas where the crop thinner or slower to develop and investigate those areas thoroughly. Check hillsides and hilltops carefully. In situations with lower populations they will often be in patches. If an area is completely eaten off the cutworms will be in the green fringes surrounding the bare patch. Army cutworms will often climb up and eat on the plant above ground so look for plants that look like they have been trimmed off. Finally look for dead and dried up plants and leaves. It is important to note that fields that had lots of green material last fall will also be at risk for this species even if they are seeded to annual crops. Spring seeded crops will be far less able to withstand cutworm attacks than fall seeded crops. In the fields we investigated the cutworms were just below the soil surface, under plant material or actually up on the plants themselves. I like the thresholds from the Manitoba website http://www.gov.mb.ca/agriculture/crops/insects/fad06s00.html

Damaged winter triticale from northeast corner of Lethbridge County. Shelley Barkley

It is possible that we will have other species of cutworm show up later this spring that did not lay their eggs on green plant material last fall so we will have to be on the watch for cutworms in other situations as well as the season progresses.

Chemical control is pretty straight forward. Check the Alberta Crop Protection Guide 2013 http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex32 for your options. In the field we saw a number of parasitoids actively searching for cutworms. Usually outbreaks of army cutworms are only last a single year because of the rapid build-up of natural enemies. Do not spray to control populations and only spray if you need to protect your crop once thresholds are reached.

Parasitic wasp found in field infested with army cutworms. Shelley Barkley

  • To see the cutworm map go to www.agriculture.alberta.ca/bugs-pest and click on the cutworm
  • To report a cutworm field click on the link under “NEWS” at www.agriculture.alberta.ca/bugs-pest
  • Remember we still need cutworms for research (including some interesting new seed treatments) so let us know if you find cutworms in your fields and we will get out and collect some.
 

Scott Meers

Scott Meers is insect management specialist with Alberta Agriculture and Rural Development. Find him on Twitter as @ABbugCounter

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